This invention relates generally as indicated to a method of plunge milling for removing large amounts of material from a workpiece blank.
Plunge milling is commonly viewed as an extremely efficient method for removing large amounts of material (e.g., 20% to 60% or more than traditional peripheral milling methods) from a workpiece blank. In such a milling process, a cutting tool is plunged axially and repeatedly into the workpiece blank in a series of overlapping passes to create an intermediate workpiece. The intermediate workpiece is then de-roughed and finished to create the final workpiece. Plunge milling is distinct from the more traditional peripheral milling methods where a cutting tool with one or more side cutting elements is moved transversely with respect to its rotational axis such that cutting occurs at the periphery of the rotating cutting tool rather than at the axial end of the cutting tool in the case of plunge milling.
An axial cutting tool typically comprises a spindle and a holder which carries cutting elements. The cutting elements are almost always replaceable inserts as they are the high-wear items in a plunge milling system. In any event, a plunge cutting tool can have as few as one cutting element, but usually has a plurality of cutting elements arranged around the circumference of the holder. The cutting elements are designed and arranged on the holder so that their axial edges form the cutting surfaces. Thus, for example, in a vertical plunge milling arrangement, the bottom edge of the cutting element defines its cutting surface.
The spindle of the axial cutting tool is attached to a feed mechanism for controlled rotational and axial movement of the axial cutting tool. During a plunge milling operation, a radially outer edge portion of the rotating axial cutting tool is aligned with a to-be-removed region of the workpiece blank and moved axially so that the cutting elements engage the material. The rotation of the cutting elements removes the material in crescent-shaped cuts and the axial movement continues until the tool reaches a predetermined stop-pass position. Accordingly, material is removed from the workpiece blank in a straight axial path.
Upon reaching the stop-pass position, the tool is axially retracted and then shifted laterally for alignment with an adjacent to-be-roughed (and usually overlapping) region of the workpiece blank for another pass of the cutting tool. These passes can be continued along the length of the workpiece. To prevent any interference between the cutting inserts and the workpiece blank during the retracting movement, the tool can be shifted laterally outward just prior to retraction.
A hallmark characteristic of plunge milling has conventionally been that the axial cutting tool moves only in the axial direction while in engagement with the material. This concentration on axial tool movement during cutting, and the avoidance of transaxial movement, has traditionally been viewed as important to increasing material removal rates and prolonging tool life.
The present invention provides a plunge milling method wherein an axial cutting tool is moved both axially and transaxially while in engagement with the workpiece material. Thus, this method of xe2x80x9ccontourxe2x80x9d plunge milling completely contradicts the conventional straight plunge milling characteristic of limiting xe2x80x9ccuttingxe2x80x9d tool movement to only the axial direction. When compared to traditional plunge milling techniques, the method of the present invention has demonstrated dramatically increased (e.g., 200%) material removal rates, a significant reduction in wear-and-tear on the milling system, and an intermediate product shape that is much closer in appearance to a desired final profile. In some applications, contour plunge milling also can be used for finishing operations.
More particularly, the present invention provides a method for effecting rapid removal of material from a workpiece blank during a rough cutting procedure. The method comprises the conventional plunge milling steps of rotating an axial cutting tool about an axis and moving the tool along said axis and into engagement with the workpiece blank for cutting material therefrom. The method further comprises the step of also moving the tool transaxially and simultaneously with the axial movement when the tool is engaged with the workpiece blank. In this manner, material is removed from the workpiece blank along a curved path.
The method of the present invention can be performed by a system comprising the axial cutting tool, a feed mechanism for the tool, and a controller which is programed to provide the axial and transaxial movement of the cutting tool. Significantly, the plunge milling method of the present invention may be performed with a conventional plunge milling system with the controller being re-programmed to accomplish the desired cutting paths. Accordingly, replacement of existing equipment (other than the controller""s motion instructions) can be avoided thereby minimizing capital expenditures. Also, the same equipment can be used to perform both the method of the present invention and traditional plunge milling methods.
These and other features of the invention are fully described and particularly pointed out in the claims. The following description and annexed drawings set forth in detail a certain illustrative embodiment of the invention, this embodiment being indicative of but one of the various ways in which the principles of the invention may be employed.